Ubuntu 20.10 (Groovy Gorilla) has reached end of life, so this bug will
not be fixed for that specific release.
** Changed in: linux (Ubuntu Groovy)
Status: In Progress => Won't Fix
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https://bugs.launchpad.net/bugs/1934489
Title:
Make Intel GPUs choose YCbCr420 encoding automatically when required
for 4k 60Hz output
Status in linux package in Ubuntu:
Incomplete
Status in linux source package in Groovy:
Won't Fix
Status in linux source package in Hirsute:
Fix Released
Bug description:
SRU Justification:
Impact:
On some setups, while the monitor and the GPU support display modes with
pixel clocks of up to 600MHz, the connector might not. This prevents RGB
encoding for 4k60Hz, but YCbCr420 encoding might still be possible. However,
which color mode is used is decided before the pixel clock capabilities are
checked, causing the check to fail and discarding 4k60Hz from the list of
possible display modes.
Fix:
This patch fixes the problem by retrying to find a display mode with YCbCr420
enforced and using it, if it is valid. It's very similar to a patch submitted
to amdgpu which fixed the same problem.
Testcase:
I personally tested on a Clevo NV40MB, but generally: Find a PC with a
current Intel iGPU, but only a HDMI 1.4 output. Connect a 4k@60Hz display
supporting YCbCr420 encoding to the HDMI port. Without the patch the maximum
that can be set via xrandr is 3840 × 2160 30Hz. With the Patch 3840 × 2160 60Hz
can be selected which will use YCbCr420 automatically.
Prerequisite (included in this email patchset as 1/4):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3c4442aa22878091f16c8d9592f5f5b6a94d1556
Patchset already got accepted upstream and reached the torvalds tree:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=eacba74d4d561ea6487d944417526e1b025cbebd
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=84d95f77f4aea3f22a486cd04777afd4ab0f0ea5
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=388b863509f76f6a5ecedd7ffdaf184aa813241e
and needs only a minor modifications to apply to ubuntu-focal/hwe-5.8
Commit-hashes:
3c4442aa22878091f16c8d9592f5f5b6a94d1556
eacba74d4d561ea6487d944417526e1b025cbebd
84d95f77f4aea3f22a486cd04777afd4ab0f0ea5
388b863509f76f6a5ecedd7ffdaf184aa813241e
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